Transformers worksheet with answers

Free printable Transformers worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy

An ideal transformer has 120 turns on its primary winding and 960 turns on its secondary winding. The primary is connected to a 400 V AC supply. Find the secondary voltage V₂.

N₁ = 120N₂ = 960V₁ = 400 V

V₂ = V

2.Easy

An ideal transformer has 100 turns on its primary winding and 200 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V₂.

N₁ = 100N₂ = 200V₁ = 690 V

V₂ = V

3.Medium

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 480 V applied to its primary winding. A 15 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 2:1V₁ = 480 VR_L = 15 Ω

I₁ = A

4.Medium

A single-phase 100 kVA, 2400/240 V transformer operates at its rated load. Treat it as ideal. Find the current I_LV in the low-voltage winding.

S = 100 kVAV₁ = 2400 VV₂ = 240 V

I_LV = A

5.Hard

A single-phase 75 kVA transformer has a core loss of 600 W and a copper loss of 1800 W at rated load. It supplies 50% of its rated kVA at a power factor of 0.8 lagging. Find the total losses P_loss in watts at this load.

S = 75 kVAP_core = 600 WP_cu,fl = 1800 Wx = 0.5pf = 0.8

P_loss = W

6.Hard

A single-phase 500 kVA transformer has a core loss of 4000 W and a copper loss of 8000 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 500 kVAP_core = 4000 WP_cu,fl = 8000 W

S_η,max = kVA

Answer key

1. V₂ = 3200 V
2. V₂ = 1380 V
3. I₁ = 8 A
4. I_LV = 416.7 A
5. P_loss = 1050 W
6. S_η,max = 353.6 kVA

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